$f(x) = -7x-1$ $f\Big($
Solution: We need to solve an equation with the function's formula $-7x-1$ on one side and the given output $-8$ on the other side. $\begin{aligned} -7x-1&=-8\\\\ 7&=7x\\\\ 1&=x\end{aligned}$ Therefore, $f(1)=-8$.